The slight brightness of the amp was cured by changing tubes in my dac. No 6922 did that trick. I added adapters and 5670s. A huge improvement to overall tone and soundstage . No fatigue on my treble sensitive ears now. Everything seemed to slow down. Beautiful clarity maintained. Loving the iha6 with the zmf or the he560. It is an amazing upgrade from my previous amps. Anyone with a tube based dac that implements the 5670 series should give the iha6 an audition.